Using a mixer, combine sour cream, eggs and vanilla until smooth. Add almond flour, coconut flour, sugar alternative, baking powder, cinnamon and salt. Blend until smooth.
Spread half the batter in pan. In a small bowl, whisk together chopped apple, sugar alternative and cinnamon. Sprinkle half of this mixture over the batter. Spread remaining batter in the pan and sprinkle with remaining filling, pressing down lightly.
Bake 50-60 minutes, watching towards the end of baking time to make sure top does not overbrown. Bread is done when a toothpick inserted into the center comes out clean. Remove from oven and cool in pan.